Current cameras are capable of automatically performing important operations for photography such as exposure determination and focusing, and hence it is highly unlikely even for a person who is unskilled in camera operation to commit a photography failure. Recently, advances have been made in an image blur compensation apparatuses which compensate for image blur caused by e.g. camera shake applied to cameras. There are, therefore, hardly any factors that induce photography mistakes by photographers.
An image blur compensation apparatus will be briefly described below. Vibration (camera shake) caused by hand movement during photography is generally vibration of about 1 Hz to 10 Hz. A basic method which can photograph pictures without any image blur even at the occurrence of such camera shake at the time of shutter release is to detect the above camera shake caused by hand movement and move the compensation lens of the camera in accordance with the detection value. Therefore, in order to photograph a picture without any image blur even at the occurrence of camera shake, the first requirement is to accurately detect camera shake, and the second requirement is to compensate for a change in optical axis due to the camera shake.
In principle, camera shake detection can be performed by equipping a camera with a means for detecting an acceleration, angular acceleration, angular velocity, angular displacement, or the like and arithmetically processing the resultant output for camera shake compensation as needed. An image blur compensation apparatus which shifts the photographing optical axis is driven on the basis of the arithmetic processing result, thereby suppressing image blur (compensating for image blur).
FIG. 12 is a perspective view showing an example of a digital compact camera. A camera body 43 comprises a release button 43a, a mode dial (including a main switch) 43b, a retractable electronic flash 43c, and an apparatus (not shown) which prevents the above image blur. Although not seen from the angle of the camera body 43 shown in FIG. 12, a liquid crystal monitor is provided on the back surface of the camera body 43. The liquid crystal monitor functions as an electronic viewfinder. The user can perform photography while checking, on the liquid crystal monitor, an image to be sensed by an image sensing device (to be described later). Activating the above image blur compensation apparatus in this photographing operation makes it possible to compensate for image blur in the camera vertical direction (pitch direction) 42p relative to an optical axis 41 and image blur in the horizontal direction (yaw direction) 42y. 
FIG. 13 is a perspective view showing the arrangement of the main part of the image blur compensation apparatus mounted in the camera body 43 in FIG. 12. Referring to FIG. 13, reference numeral 52 denotes a compensation lens which is an optical system for compensating for image blur; and 53, a holding frame which holds the compensation lens 52. Reference numeral 50 denotes an image blur compensation apparatus which comprises the compensation lens 52, the holding frame 53, and the like and compensates for image blur in the pitch direction 42p and image blur in the yaw direction 42y shown in FIG. 12 by being freely driven in the directions indicated by arrows 58p and 58y. This apparatus will be described in detail later. Reference numerals 45p and 45y denote camera shake detection units, respectively, which comprise angular velocity meters, angular acceleration meters, or the like which detect camera shake around arrows 46p and 46y. Reference numeral 44 denotes an image sensing device. Outputs from the camera shake detection units 45p and 45y are transformed into driving target values for the image blur compensation apparatus 50 through arithmetic circuits 47p and 47y (to be described later). When the driving target values are input to the coils of the image blur compensation apparatus 50, image blur compensation is performed.
FIG. 14 is a block diagram showing the camera shake detection unit 45p and the arithmetic circuit 47p shown in FIG. 13. Since the arithmetic circuit 47y has the same arrangement as that of the arithmetic circuit 47p, only the arithmetic circuit 47p will be described in detail below.
In the following description, the term “image blur compensation apparatus” sometimes indicates an overall mechanism for image blur compensation, including the camera shake detection units 45p and 45y, the arithmetic circuits 47p and 47y, and the like in addition to the image blur compensation apparatus 50.
The arithmetic circuit 47p includes a DC cut filter/amplifier 48p, a low-pass filter/amplifier 49p, and an A/D conversion unit 410p which converts an analog signal into a digital signal, as indicated by the area enclosed by the chain line. The arithmetic circuit 47p further includes a camera microcomputer 411 and a known driving circuit unit 420p comprising a PWM (Pulse Width Modulation) driver and the like. The camera microcomputer 411 includes a storage unit 412p, differential amplifier 413p, DC cut filter 414p, integrating unit 415p, responsiveness adjusting unit 416p, storage unit 417p, differential amplifier 418p, and PWM duty transform unit 419p. Note that a DC means a direct current.
In this case, the camera shake detection unit 45p includes a camera shake gyro sensor which detects the camera shake angular velocity. The camera shake gyro sensor is driven in synchronism with ON operation of the main switch of the camera to start detecting a camera shake angular velocity applied to the camera. The DC cut filter/amplifier 48p comprising an analog circuit in the arithmetic circuit 47p cuts off a DC bias component superimposed on an output signal from the camera shake detection unit 45p, and amplifies the signal as needed. The DC cut filter/amplifier 48p has a frequency response that cuts off signals with frequencies of 0.1 Hz or less so as to avoid influences on a camera shake frequency range of 1 Hz to 10 Hz applied to the camera. If, however, the DC cut filter/amplifier 48p is designed to have a frequency response that cuts off signals of frequencies of 0.1 Hz or less, it takes about 10 sec to completely cut off DC bias components after a image blur signal is input from the camera shake detection unit 45p. For this reason, the time constant of the DC cut filter/amplifier 48p is set to be small (for example, is set to a response frequency that cuts off signals of frequencies of 10 Hz or less) until, for example, 0.1 sec after the main switch of the camera is turned on, thereby cutting off DC bias components for a short period of time, e.g., about 0.1 sec. Thereafter, the time constant is increased (to have a frequency response that cuts off only signals of frequencies of 0.1 Hz or less) to prevent a camera shake angular velocity signal from deteriorating due to the DC cut filter/amplifier 48p. 
An output from the DC cut filter/amplifier 48p is amplified by the low-pass filter/amplifier 49p comprising an analog circuit in accordance with the A/D resolution of the A/D conversion unit 410p, as needed. In addition, high-frequency noise superimposed on the output (i.e., the camera shake angular velocity signal) is cut off. This operation is performed to prevent a read error of a camera shake angular velocity signal due to noise in the camera shake angular velocity signal in sampling operation performed by the A/D conversion unit 410p when the camera shake angular velocity signal is input to the camera microcomputer 411. The signal output from the low-pass filter/amplifier 49p is sampled by the A/D conversion unit 410p on the next stage and is input to the camera microcomputer 411.
Signal processing in the camera microcomputer 411 will be described below. The DC bias components of a camera shake angular velocity signal are cut off by the DC cut filter/amplifier 48p described above. Thereafter, however, DC bias components are superimposed on a camera shake angular velocity signal due to amplification by the low-pass filter/amplifier 49p, and hence it is necessary to perform DC bias component cutting (to be also referred to as “DC cutting” hereinafter) in the camera microcomputer 411. Therefore, for example, a camera shake angular velocity signal sampled 0.2 sec after the camera main switch is turned on is stored in the storage unit 412p, and the differential amplifier 413p obtains the difference between the stored value and the camera shake angular velocity signal, thereby performing DC cutting. Note that in this operation, since DC bias components can only be roughly cut off, the DC cut filter 414p comprising a digital filter on the subsequent stage further performs sufficient DC cutting. The reason why the differential amplifier 413p can only roughly perform DC cutting is that a camera shake angular velocity signal stored 0.2 sec after the camera main switch is turned on contains not only DC components but also actual camera shake. The time constant of the DC cut filter 414p can also be changed like the analog DC cut filter/amplifier 48p. The time constant of the DC cut filter 414p is gradually increased 0.2 sec after a lapse of 0.2 sec since turning-on of the main switch of the camera. More specifically, the DC cut filter 414p has a filter characteristic that cuts off frequencies of 10 Hz or less after a lapse of 0.2 sec since turning-on of the main switch. Subsequently, the cutoff frequency of the filter is decreased every 50 msec like 5 Hz>1 Hz>0.5 Hz>0.2 Hz. When the photographer half-presses the shutter release button (turns on sw1) during the above operation to start photometry and distance measurement, photography can be immediately performed, and it may not be desirable to consume much time to change the time constant.
In such a case, the operation of changing the time constant is stopped halfway in accordance with a photographing condition. If, for example, it is determined from a photometry result that the photographing shutter speed is 1/60, and the photographing focal length is 150 mm, the image blur compensation accuracy need not be very high. The DC cut filter 414p therefore finishes changing the time constant when the time constant is changed up to a characteristic that cuts off frequencies of 0.5 Hz or less (controls the time constant change amount in accordance with the product of a shutter speed and a photographing focal length). This makes it possible to shorten the time required to change the time constant, thereby giving priority to a shutter release opportunity. Assume that the shutter speed is higher or the focal length is shorter. Obviously, in this case, when the time constant is changed up to a characteristic that cuts off frequencies of 1 Hz or less, the DC cut filter 414p finishes the changing operation. Alternatively, if the shutter speed is lower and the focal length is longer, photography is inhibited until the time constant is completely changed.
The integrating unit 415p integrates signals from the DC cut filter 414p to transform the angular velocity signal into an angular signal. The responsiveness adjusting unit 416p on the next stage amplifies the integrated angular signal, as needed, on the basis of the focal length of the camera and object distance information at that point of time, and transforms the angular signal such that the image blur compensation apparatus can be driven by a proper amount in accordance with the image blur angle. This transformation needs to be performed because the photographing optical system changes upon zooming and focusing operations and the optical axis shift amount changes with respect to the driving amount of the compensation lens 52.
When the shutter release button is half-pressed (sw1 is turned on), an operation of the image blur compensation apparatus 50 starts. At this point of time, care should be taken to prevent the image blur compensation apparatus 50 from abruptly starting image blur compensating operation. The storage unit 417p and the differential amplifier 418p are provided for this purpose. The storage unit 417p stores the camera shake angular signal from the integrating unit 415p which is obtained when the above shutter release button is half-pressed. The differential amplifier 418p obtains the difference between the signal from the integrating unit 415p and the signal from the storage unit 417p. When the shutter release button is half-pressed, the two signal inputs to the differential amplifier 418p are equal to each other, and a driving target value signal from the differential amplifier 418p to the image blur compensation apparatus 50 is zero. Thereafter, a predetermined value is continuously output as a driving target value signal (i.e., the storage unit 417p serves to set the integration signal as the origin when the shutter release button is half-pressed). This prevents the image blur compensation apparatus 50 from abruptly starting to be driven.
The target value signal from the differential amplifier 418p is input to the PWM duty transform unit 419p. When a voltage or current corresponding to the camera shake angle is applied to the coil provided in the image blur compensation apparatus 50, the image blur compensation apparatus 50 (the compensation lens 52 and the holding frame 53) is driven in accordance with the camera shake angle. The image blur compensation apparatus 50 is preferably driven by PWM to save the driving power consumption of the compensation lens 52 and the power consumption of a drive transistor for the coils. For this reason, the PWM duty transform unit 419p changes the duty for coil driving in accordance with the target signal value. For example, in the case of PWM using a frequency of 20 kHz, the duty is set to “0” when the target signal value from the differential amplifier 418p is “2,048”, and to “100” when the target signal value is “4,096”. Then, the range between these duties is divided into equal parts so that the duty is determined in accordance with the target signal value. Note that the duty determination may be precisely controlled based not only on the target signal value but also on the current photographing conditions for the camera (including the temperature, the posture of the camera, and the state of the battery), so as to realize accurate image blur compensation.
An output from the PWM duty transform unit 419p is input to the known driving circuit unit 420p comprising a PWM driver and the like, and an output from the driving circuit unit 420p is applied to the coil provided in the image blur compensation apparatus 50, thereby performing image blur compensation. The driving circuit unit 420p is activated in synchronism with the timing at which 0.2 sec elapses after the shutter release button is half-pressed.
Although not shown in the block diagram of FIG. 14, even when the photographer fully presses the shutter release button of the camera (turns on sw2) to start exposure, since image blur compensation is kept performed, a deterioration in image quality due to blur of photographed image can be prevented. In addition, the image blur compensation apparatus 50 keeps performing image blur compensation as long as the shutter release button is half-pressed (sw1 is turned on). When the half-pressed button is released, the storage unit 417p stops storing a signal from the responsiveness adjusting unit 416p (transits into a sampling state). As a result, the signals input from the responsiveness adjusting unit 416p and the storage unit 417p to the differential amplifier 418p become equal to each other, and an output from the differential amplifier 418p becomes zero. Consequently, a zero driving target value is input to the image blur compensation apparatus 50, thus stopping image blur compensation.
The integrating unit 415p keeps performing integration unless the main switch of the camera is turned off. When the shutter release button is then half-pressed (sw1 is turned on), the storage unit 417p stores a new integration output (holds a signal). When the main switch is turned off, the camera shake detection unit 45p is turned off, thus terminating a series of image blur compensating operations.
If a signal from the integrating unit 415p becomes larger than a predetermined value, the DC cut filter 414p determines that panning of the camera has been performed, and changes the time constant of the DC cut filter 414p. For example, the DC cut filter 414p changes, for example, a characteristic that cuts off frequencies of 0.2 Hz or less to a characteristic that cuts off frequencies of 1 Hz or less, and then returns the time constant to the initial value in a predetermined period of time. This time constant change amount is also controlled by the magnitude of an output from the integrating unit 415p. More specifically, if the output exceeds the first threshold, the characteristic of the DC cut filter 414p is changed to a characteristic that cuts off frequencies of 0.5 Hz or less. If the output exceeds the second threshold, the characteristic is changed to a characteristic that cuts off frequencies of 1 Hz or less. If the output exceeds the third threshold, the characteristic is changed to a characteristic that cuts off frequencies of 5 Hz or less. When an output from the integrating unit 415p becomes very large (if, for example, a very high angular velocity is produced due to panning of the camera), the integrating unit 415p is reset to prevent arithmetic saturation (overflow).
Referring to FIG. 14, the arithmetic circuit 47p incorporates the DC cut filter/amplifier 48p and the low-pass filter/amplifier 49p. Obviously, however, these units may be incorporated in the camera shake detection unit 45p. 
FIGS. 15A to 15C show the arrangement of the image blur compensation apparatus 50 disclosed in Japanese Patent Laid-Open No. 10-181343. FIG. 15A is a front view of the image blur compensation apparatus 50. FIG. 15B is a view taken from the direction indicated by an arrow 51 in FIG. 15A. FIG. 15C is a sectional view taken along a line A-A in FIG. 15A.
As shown in FIG. 15C, the compensation lens 52 comprises two lenses 52a and 52b fixed to the holding frame 53 and a lens 52c fixed to a base plate 54, and serves as part of the photographing optical system.
A yoke 55 made of a ferromagnetic material is mounted on the holding frame 53, and permanent magnets 56p and 56y made of neodymium or the like are fixed onto the behind of the yoke 55 by magnetic attraction (see FIG. 15C). In addition, three sustention axes 53a radially extending from the holding frame 53 at equal angular intervals (at 120° intervals) are fixed in long holes 54a formed in a side wall 54b of the base plate 54 (see FIG. 15A).
As shown in FIG. 15B, in consideration of the relationship between the sustention axes 53a and the long holes 54a, since they are fitted in the direction of an optical axis 57 (see FIG. 15C) of the compensation lens 52, the sustention axes 53a do not move around. In contrast, the long holes 54a extend in the direction perpendicular to the optical axis 57. Therefore, the holding frame 53 is prohibited from moving in the direction of the optical axis 57, but can freely move within a plane perpendicular to the optical axis 57 (in the directions indicated by arrows 58p, 58y, and 58r shown in FIG. 15A). However, since extension coil springs 59 are provided between pins 53b on the holding frame 53 and pins 54c on the base plate 54, the movement of the holding frame 53 in the respective directions (58p, 58y, and 58r) is elastically prohibited.
As shown in FIG. 15A, coils 510p and 510y (partly indicated by the broken lines) are attached to the base plate 54 so as to face the permanent magnets 56p and 56y. The yoke 55, permanent magnet 56p, and coil 510p are arranged as shown in FIG. 15C (the permanent magnet 56y and the coil 510y are arranged in the same manner). When a current is supplied to the coil 510p, the holding frame 53 is driven in the direction indicated by the arrow 58p. When a current is supplied to the coil 510y, the holding frame 53 is driven in the direction indicated by the arrow 58y. The driving amounts of the holding frame 53 are determined by the balances between thrusts produced in association with the spring constants of the extension coil springs 59 in the respective directions and the coils 510p and 510y and the permanent magnets 56p and 56y. That is, the displacement (shift) amount of the compensation lens 52 can be controlled on the basis of the amounts of currents supplied to the coils 510p and 510y. 
The image blur compensation apparatus 50 described above is mounted in a camera, and hence is required to be efficiently driven while suppressing power consumption to a minimal. In addition, in a recent digital camera, the image sensing device 44 has greatly reduced in size. As the size of image sensing device 44 decreases in this manner, the image blur compensation apparatus 50 inside the camera is required to be driven with higher accuracy.
As another associated technique, an image blur compensation apparatus designed to improve the driving efficiency by optimally setting a driving force in each direction has also been proposed (see Japanese Patent Laid-Open No. 10-174470). In addition, there has been proposed an image blur compensation apparatus designed to perform driving in two directions by using driving means arranged at 120° intervals, which can realize efficient driving by generating different resultant forces in different directions, e.g., aligning the resultant forces in a direction in which large image blur has occurred. For reference, see Japanese Patent Laid-Open No. 5-257088.
The following problem arises in the image blur compensation apparatus disclosed in Japanese Patent Laid-Open No. 10-174470. Although driving load based on the weight of the image blur compensation apparatus is distributed to the driving means in a well-balanced manner, a pair of driving means differ in driving force and type. For this reason, when the two driving means are driven for free driving operation in the two axis directions, accurate driving operation cannot be performed.
The following problem arises in the image blur compensation apparatus disclosed in Japanese Patent Laid-Open No. 5-257088. Since a compensation lens is moved (swung) by being biased by a motor and a driving lever, a deterioration in response is caused by backlash between the compensation lens and the driving lever or a deterioration in driving accuracy due to friction.
In addition, in each of the image blur compensation apparatuses in the Japanese Patent Laid-Open Nos. 10-174470 and 5-257088, each driving means is not designed to be provided on the member which holds the compensation lens so as to be integrally driven, and hence it lacks in accuracy and response.